1. Field of the Invention
The present invention relates to intermittently active radio frequency identification (RFID) tags to locate, track, control, and recognize animate or inanimate objects.
Definitions: As used herein, the following terms have the following meanings, unless otherwise specified:                RFID: radio frequency identification        Tag: an active miniature RFID tag        Controller: a portable controller, a wearable controller, a central control unit        Signal: beep, chirp, light etc., mechanical, display with arrow or symbol, silent (stealth) logged and sent wirelessly later or sent wirelessly directly        Button or switch: tactile switch, membrane switch, capacitive switch        Input interface: a button, multiple buttons, a combination of buttons        Take Action” or (“Action”): one or combination of internal tag operations, such as logging, counting, storing data, and changing its configuration, that do not produce signals; and/or signaling, which includes, a beep, a chirp, a light etc., mechanical, display with arrow or symbol, silent (stealth) logged and sent wirelessly.All other terms used herein not specified above shall be understood to have their common meaning as used and understood by those of skill in the art and in the relevant industry.        
2. Background of the Invention
There is a long-standing use of radio frequency identification (RFID), starting in the 1960s with the SICARID (Siemens Car Identification), which uniquely identified train car wagons and car parts in production. That technology used passive RFID: a tag on the object is irradiated with RF waves from an RFID reader; the tag then uses the energy to emit an RFID signal back to the RFID reader that contains its identification, location or other data. The RFID reader receives the RFID tag information. Passive RFID tags can also store parts of that signal's energy in a temporary power storage unit, such as a capacitor, to do calculations, access memory, and create their own RF signals. Passive tags are now applied to almost any stationary or moving objects, including people to identify in near field.
Over time, RFID technology has developed active RFID tags. Active RFID tags can also detect and receive an RF signal directly from a reader and store parts of the incident RF energy, but they have an independent onboard power source, such as a battery, or are connectable to one. They can thus transmit the RF signal autonomously, at a selected time or at programmed triggers, as from a temperature sensor. Their onboard power source also gives them a longer range than passive RFID tags. Another difference is that active RFID tags are not restricted to one-directional communication of the same bits of information, i.e., the same packet per transmission, like a garage door opener, for example, which can only transmit one instruction, “open/close.” Active RFID tags can transmit more complex information, such as conducting sessions (send/receive) for authorization as a challenge-response exchange, as well as for acknowledgements and retransmissions. Active RFID tags are familiar as toll collection transponders for ETC (Electronic Toll Collection), as used in the E-Z Pass bridge toll in the U.S.
All active and passive RFID tags consist of an antenna, reception and transmission components, and a processing unit or circuit to perform calculations, such as accessing memory to read or store data. A typical RFID tag can hold up to several kilobytes of data, for example, a license tag with a serial number. Active and passive RFID tags and their readers do not need to be “in line of sight” with each other to communicate. Examples are keyless entry systems in vehicles and ID “chips” implanted in animals. The state of the art of range for both active and passive RFID tags is several meters, but passive tags only accomplish this range at very narrow angles of the antennas to each other.
Both active and passive RFID have been developed for specific and generally in-house or local purposes, like toll collection (active) or shoplifting detection (passive). Agreements across systems and other attempts at standardization are in the works, as with RFID specification EPC Gen 2 UHF (ISO/IEC 18000-6) defining a wireless protocol for both active and passive RFID for possible interchangeability between developed systems.
As RFID technology has evolved, it has become miniaturised. Recently, passive RFID tags have become as small as 0.05 mm by 0.05 mm, and thin as a sheet of paper. However, active RFID tags are expensive. Active RFID tags cost from 10 to 50 cents (US) each, and RF signal readers cost up to US $1,000 each. These costs are especially prohibitive when RFID is put to its logical use of supply chain tracking, which requires significant numbers of readers and RFID tags. Even passive RFID systems have proved too expensive for large-scale use. Retailing giants like WalMart, with over 20,000 suppliers, have gone from insisting that all suppliers' products have RFID tags to only using RFID for in-store tracking. The US Department of Defense (DoD) underwent a similar change: after mandating RFID in 2003 for supply logistics, the DoD dropped that requirement in favor of implementing more GPS-based technology. In addition to budget considerations, there were concerns that RFID was not efficient and not accurate for bulk liquids and metal (NDIA (National Defense Industrial Association), May 2007, “Tracking Military Supplies No Longer Requires RFID” Sandra I. Erwin—same source for Walmart data). On the other hand, the Department of Defense continues to issue RFI and RFP requests because of the inherent utility of the technology, but the requirements are high and the DoD is seeking multiple suppliers and vendors (RFID Journal, Aug. 28, 2006, “DOD Issues RFP for RFID” Mary Catherine O'Connor), which shows that the DoD does not wish to give up on this technology but has grasped the difficulties in creating a versatile, reliable and economic system.
Thus, in respect to cost, available active RFID is no real improvement over passive RFID and remains limited to isolated systems. Active RFID tag technology has yet to fulfil its potential. It lacks the versatility to adapt to myriad different situations. RFID readers are still large, about the size of a larger PDA with a hand-sized antenna attached to generate the required RF field. Another issue is that some applications, transmitting over a longer range, require the RF beam to be aimed in the direction of the active target RFID tags; an application needing an omnidirectional signal will have a much shorter range. Thus, active RFID tag technology remains limited to specific purposes in defined physical areas. Even at its most mobile, the technology can only communicate with matching active RFID tags in passing cars; in that case, only the RFID tag, not the reader, is mobile, and there are still on-going concerns about the accuracy of these RFID tag/reader devices.
3. Prior Art
The use of active RFID tags for locating objects is known in the art. The RFID tags are attached to an object; a reader is then used to locate the object by a wireless transmission to the RFID tag, activating it with the wireless energy and reading the response that the RFID generates from the incident energy and the RFID reader determining the signal strength of the response so as to deduce the distance.
U.S. Pat. No. 6,600,418 is directed to warehouse management and discloses fitting RFID tags onto objects and/or fixed locations that enable a specially equipped vehicle to find objects or place the tagged object. The RFID tags carry information on the identity and location of objects in the warehouse. The driver of the vehicle, such as a forklift, can track down an object without having to leave the vehicle to do bar code scans. The operator is guided by lights, audible beeps, or a graphics display integrated into the vehicle. This system is limited to inventory and shipping-related tasks, and also requires a central computer. Overall, this invention is directed to specific conditions, a vehicle and mechanical locomotion to store and retrieve objects. This invention does not disclose details about the power management of the active RFID tags nor how their information is calculated into a location. This system is of limited practicality, since it is dedicated to large-scale warehouse inventories.
U.S. Pat. No. 6,661,335 discloses an asset management system with fixed sensors and readers in a building to track a moveable asset that has an RFID tag called a transponder. The sensors track the object's movements and location by sending signals back to a processor/computer system. The system is not miniature because it contains three antenna coils, one in each xyz direction, and each must be directional, as required by the invention. Hence, the tracking devices are larger than RFID tags using an omnidirectional antenna. The invention is portable in principle but would be cumbersome. Unlike the '335 patent, our invention disclosed herein is truly miniaturized and designed for portability and versatility; it achieves the same range with an omnidirectional antenna, independently of the direction the RFID tags or controller are positioned.
U.S. Pat. No. 6,396,438 discloses the use of stationary sensors that can determine the position of an RFID transponder. The sensors have a plurality of antenna coils arranged in unique physical orientations to transmit RF signals of differing phases; the transponder receives these signals and compares the phase of at least two to determine the relative position of the transponder. The system requires a minimum size, determined by the wavelength of the frequencies used: 400 MHz and 2.4 GHz, requiring a device 3-16 cm in size. The minimum distance of the antennae for a phase shifted signal as described in this frequency range is also 3-16 cm. The '438 patent, unlike the present disclosure, relies on multiple antenna coils permanently affixed in a structure; the present disclosure is a system that is portable, calculates positions through triangulation and signal strength of at least two RFID tags, and can add run time differences. It can also work with a single tag calculating distance through signal strength and also can add run time differences.
U.S. Pat. No. 7,405,663 discloses a system for detecting RFID tags in an exit control system to prevent the unauthorised removal of tagged objects. A plurality of antennae radiate power to tags within the protected area, which is described as an interrogation corridor, a large, complex system integrated into a building. This invention uses passive RFID but is more complex than a passive anti-theft tag system commonly found at the doorways of shops, for example, as it covers an area approaching the exit and can specifically identify the object being removed. This patent requires a complex system fixed into a structure. The system cannot track in “open air” and is not itself mobile. The invention we disclose is active RFID and does not require a homogeneous or distributed RF signal in an area to power up RFID tags that are nearby; it powers up using its own onboard source independently of any wireless signal.
U.S. Pat. No. 7,274,292 discloses a proximity management system around a central control device, which can be realised as a wireless communication device, including a cellular or wireless telephone, a personal digital assistant (PDA) or a handheld portable communication device. The '292 patent uses a computer to group tagged objects by purpose, such as “work” or “camping.” The system tells the user when the objects in a selected group are either within or beyond a pre-set radius. Each object has its own identifier and a graphical user interface displays the groups and objects for selection as well as information about the location of these objects. An essential feature of this technology is the graphical interface and computer, which allow data entry of individual/associated objects and then creating the groups the user desires. The '292 does not discuss the design of the wireless protocol nor disclose whether the devices communicate in a synchronized protocol. Although the patent claims that the controller knows the geographic location of objects, there is no detailed information on how this occurs. In effect, the invention is a sophisticated electronic “reminder” system designed to inform the user whether a desired set of tagged objects (“vacation”) are in proximity to the user, for a kind of roll-call prior to departure. Some objects may be used only once a year, which raises questions about battery life. An additional shortcoming in this and similar inventions is that the central control, much as with television remote controls, must itself be found first. Finally, an essential feature in the '292 patent is the graphical user interface to configure and operate the system, which is complex and makes the device at least cell phone size. Our invention differs because it allows true searching and locating, as well as controlling and recognition functions, and it does so with just two miniaturized circuits that are integratable into a ring or other object that is always with the user.
U.S. Pat. No. 7,242,293 discloses a proximity alert system that is connected to a human or robotic hand to alert a caretaker or observer when the hand is too close to a tagged object. For this specialized purpose, the '293 apparatus is limited to a very short range of 25 centimeters, and is only deployed in a very specialized field of use.
Given these shortcomings, as well as those described in the introduction, it is non-obvious to look to active RFID as a reliable, versatile system that can be adapted to locate, track, control and recognize objects. While passive RFID is accepted in passports and other devices, these remain limited to local systems and specific purposes. GPS, even with its own limitations, including requiring a satellite link, lack of precision (finding an object in a room), and signal issues (inoperable in a basement, for example), is actually edging out existing RFID applications.